Aluminous abrasive.



THOMAS 1B. ALLEN, OF TORONTO, CANADA, ASSIGNOR TO THE CARBORUNDUM COMPANY, OF NIAGARA FALLS, NEW YORK, A. CORPORATION OF PENNSYLVANIA.

ALUMINOUS ABRASIVE.

No Drawing.

To all whom it may concern:

Be it known that I, THOMAS B. ALLEN, a subject of the King of Great Britain, residing at Toronto, Canada, have invented a new and useful Improvement in Aluminous Abrasives, of which the following is a full, clear, and exact description.

This invention relates to a new and useful improvement in the manufacture of aluminous abrasives. Aluminous abrasives are now commonly made by the use of an electrically developed heat process usually consisting in subjecting aluminous ore such as emery, bauxite or clay, usually with the addition of a reducing agent, such as carbon, to heat in an electric furnace until the product is fused and then allowing it to cool and crystallize. These electrically prepared abrasives have a wide field of usefulness, nevertheless despite their great efficiency they have not succeeded in displacing the natural emery in a variety of grinding and polishing operations since they aredistinguished from the latter not only in their chemical com-position but also in their physical. properties. They are in general of greater hardness and toughness than natural emery and for this reason certain grinding operations are best accomplished by the natural abrasive and with more economical results.

In the manufacture of artificial abrasives by electricallydeveloped heat there are always present both in microscopic and macroscopic amounts certain impurities usually.

of a metallic nature or having the characteristics of reduction products, which result from the reduction of impurities in the aluminous ore either by added carbonaceous material or by the action of the electrodes. These impurities are usually compounds of metallic iron with silicon, titanium or other elements and must be removed substantially before an abrasive of satisfactory properties can be produced, because usually their presence causes great difficulty in the manufacture of suitable grinding and polishing articles, especially in the proper binding of the abrasive grain. Furthermore, electrically prepared abrasives are very expensive,

due to the high cost of electrodes, electric energy and the maintenance cost of electric furnace operations. Moreover the1r manufacture IS llmlted to those regions where a Specification of Letters Patent.

Patented June 4, 1918.

plentiful supply of electric energy and other necessities exists.

I have discovered that I can produce a crystalline artificial aluminous abrasive material resembling natural emery in some characteristics and can avoid all the difficulty inherent in electrically prepared abraslves by subjecting aluminous ore or aluminous mixture to fuel heat or heat generated in a combustion furnace and I have found that the combustion of fuel, oil preferably, under stron ly reducing conditions gives good results 1n this method. In choosing a suitable mixture for melting, it is necessary to consider the abrasive qualities such as hardness, toughness and fracture that are desired. These properties are determined by the proportion of the components of the mixture and by the chemical composition of the components. I have found that substances containing from to 85% of alumina, and 10% to 20% iron oxid, 3% to 10% of silica and 2% to 5% titanium ox'd yield a satisfactory product. I prefer to take as a raw material a bauxite ore consisting after calcining of about alu mina, 10% iron oxid, 7% silica and 3% titanium oxid. Such an ore is readily selected from available. bauxite ores or may be arrived at by mixing aluminous ores with the other above mentioned components. The materials are reduced to a fine state of subdivision so that all will pass through a 1} mesh and preferably finer. After thoroughly mixing they are fed into a fuel heated furnace by which a thorough heating and a partial sintering may be effected. For this purpose I have found that a rotary kiln lined with a suitable refractory lining to be preferable, acting as a pre-heater. The thoroughly heated or partially sintered ma terial is then placed in a crucible in which the final heating is accomplished. By means of oil flame a temperature of 3400 F. may be obtained and I find this is sufficient to effect the further and final fusion of the material. I find it is not necessary to have the material brought to a very liquid state; indeed for many purposes merely obtaining the material in a molten state is suficient to yield a satisfactory product. If desired, the preheating can be dispensed with and the entire operation accomplished in a single stage with the oil fuel. During the preheating and in the final heating it is preferable to have a strongly reducing atmosphere in order that the iron oxid present assume a ferrous state in which state it has a much greater fluxing ower than when in the higher state of oxldization. A final melting may be made in a graphite crucible or in a vessel lined with a suitable refractory material and the heat may be supplied indirectly or directly.

I do not limit myself to the method of heating here described and in carrying out the operation on a large scale the heat may be accomplished by playin several jets of the oil flame upon the sur ace of the mass to be heated, the new material being dropped on in powdered form under the flame and an ingot be built up making the process practically continuous. The oil flame may be displaced with a flame of powdered coal tributed abou t\them and together with the A1 0 crystals a pears to be held together with some sort 0 anisotropic matrix. This 1s colorless except'for an occasional brownish or as.

'l he material crystallizes on cooling, forming a dark crystalline mass characterized by great hardness and toughness. An examination under the microscope shows that the material consists very largely of very minute crystals of A1 0 These rarely reach a diameter of one-hundredth of a millimeter and are usually much less. There is also a large amount, approximately 25%, of finely divided black opaque material which to some extent is included in the A1 6) crystals but appears to be more generallydistalline fused aluminous abrasive material,

containing at least 60% of crystalline alumina and more than 10 per cent. of silica and oxids of iron and titanium, the major portion of the alumina crystals having an average diameter of less than one-hundredth of a millimeter.

'In testimony whereof, I have hereunto set THOMAS B. ALLEN.

my hand.

Witnesses:

SAML S. DIEMN, ARTHUR BA'rrs. 

